The present invention relates to a magnetic circuit for the stator of an electric induction motor comprising a packet of stacked laminations provided with laterally open slots adapted to receive the substantially rectilinear active portions of the turns of the winding for the poles of the motor, the surface of each slot being covered by an internal layer of an electrically insulating material molded onto the inner insulation surface of the slot whereat it forms a laterally open insulating channel for insulating said active portion of the turns housed in the slot from the body of the motor, and the layer in each slot being united with the layer of each one of the two adjoining slots at the two outer sides of the stator by an electrically insulating lateral layer, the combination of the internal layers and the lateral layers constituting a one-piece molded layer over the slot region, ensuring insulation of the slot region from the body of the motor and at least cohesion of the packet of laminations.
The stators of low and medium power electric motors carry slots into which the wires constituting the pole windings of the motor are introduced through a relatively thin slit provided between two teeth of the magnetic circuit. There is generally only a small difference in voltage between two adjoining wires of a winding, this difference being generally less than one volt in the case of fractional horse-power electric motors operating from a supply with 200/380 volts between phases, and a simple varnish insulation is sufficient to ensure the turns are insulated from each other. Insulation with respect to the conducting body of the motor at the base area of the slot must, on the other hand, not only be able to withstand the nominal supply voltage, but also be able to withstand surges and spikes resulting from switching and the like or atmospheric phenomena which can be present in the supply, and for this reason the base of the slot must be covered by a sheet of insulator, the fitting of which can often be a costly time-consuming operation.
The question of replacing the base insulator of the slot by an economical process that insulates the slot has been raised but, up until now, was not able to be resolved in a reliable manner from the electrical point of view in the case of motors such as those used for hot water circulations pumps, notably water for heating purposes, which must have a very long service life without suffering from breakdown, while being able to be supplied from any sort of three-phase or single-phase network which under exceptional conditions can receive powerful fast-rising voltage spikes of atmospheric origin, which can, for example, attain figures of ten times the single-phase network voltage (in other words 2,200 volts for the 220 volt single-phase network).
The present invention notably has the aim of resolving the problem of providing insulation for the slots at a competitive price while making the best use of the laminations of a magnetic circuit of a motor.